Summary

The improvement of organic fertilization practices is essential to increase organic potato production in the highland region of NW Portugal, with environmental benefits and better returns. For that reason, the response of organic potato was evaluated throughout a randomized block design experiment, with two cultivars (Raja and Virgo) and increasing rates of composted organic pig manure (0, 15, 30 and 45 t ha-1). These cultivars were also grown with mineral N fertilizer (120 kg N ha-1) under conventional practices to compare the results between crop systems, 30, 45, 60, 80 and 125 days after planting. Crop yield was not improved with increasing rates of compost application because the N mineralization rate of the compost was small and soil organic matter was high (8%). Organically grown cv. Virgo yielded 66.0% of the conventional crop, whereas Raja yielded 46.6%. The N uptake of the organic crop (tubers and foliage) was 37.0 kg ha-1 for Raja and 50.5 kg ha-1 for Virgo, respectively 21.1% and 27.8% of the N uptake by the same cultivars grown with mineral fertilizer. Although foliage N content was increased for the conventional crops, differences between N content of organic and conventional tubers were not significant, as well as for K, Ca and Mg.

This paper is published in the conference proceedings: Neuhoff, Daniel; Halberg, Niels; Alfldi, Thomas; Lockeretz, William; Thommen, Andreas; Rasmussen, Ilse A.; Hermansen, John; Vaarst, Mette; Lck, Lorna; Carporali, Fabio; Jensen, Henning Hgh; Migliorini, Paola and Willer, Helga, Eds. (2008) .Cultivating the Future Based on Science. Proceedings of the Second Scientific Conference of the International Society of Organic Agriculture Research (ISOFAR), held at the 16th IFOAM Organic World Congress in Cooperation with the International Federation of Organic Agriculture Movements (IFOAM) and the Consorzio ModenaBio, 18 . 20 June 2008 in Modena, Italy.. International Society of Organic Agriculture Research (ISOFAR), c/o IOL, DE-Bonn, Research Institute of Organic Agriculture FiBL, CH-Frick. https://orgprints.org/13672 and https://orgprints.org/13674